Pulp sifter with cleaning means

ABSTRACT

The sifting device consists of a chamber with an opening for feeding pulp to be sifted; a cylinder plate installed in the chamber so that it can be rotated around its axis; at least one fixed sieve cleaner with an outlet pipe open toward the sieve surface for removing reject pulp, a lower pressure prevailing in the outlet pipe than on the sieve surface; a detachment organ for reject installed in connection with the outlet pipe; and a blocking piece on the side opposite to the open part of the outlet pipe.

United States Patent 1191 Savia v 1451 Nov. 5, 1974 PULP SIFTER WITH CLEANING MEANS [75] Inventor: Risto Martti Juhani Savia,

lnkeroinen, Finland [73] Assignec: 0y Tampella Ab, Tampere, Finland [22] Filed: Mar. 21, 1972 [21] Appl. No.: 236,709

[30] Foreign Application Priority Data Mar. 25, 1971 Finland 862/71 [52] US. Cl 209/303, 209/385, 209/380 [51] Int. Cl B07b 1/52 [58] Field of Search 209/379, 380, 384, 385,

[56] References Cited UNITED STATES PATENTS 2,796,809 6 1957 Sprau .1 209/380 x 2949,187 8/1960 Owens 3,311,235 3/1967 Ahlfors 3,635,341 1 1972 Davis 210/396 x FOREIGN PATENTS OR APPLICATIONS 754,716 9/1944 Germany 209/304 1.227991 3/1960 France 210 397 574,656 3/1958 Italy 210/403 Primary ExaminerRobert Halper Attorney, Agent, or Firm-Roylance, Abrams, Berdo & Kaul [57] ABSTRACT The sifting device consists of a chamber with an opening for feeding pulp to be sifted;.a cylinder plate installed in the chamber so that it can be rotated around its axis; at least one fixed sieve cleaner withan outlet pipe open toward the sieve surface for removing reject pulp, a lower pressure prevailing in the outlet pipe than on the sieve surface; a detachment organ for reject installed in connection with the outlet pipe; and a blocking piece on the side opposite to the open part of I the outlet pipe. I

9 Claims, 3 Drawing Figures 1 PULP SIFTER WITH CLEANING MEANS BACKGROUND OF THE INVENTION Previously known is, among others, the so-called Jonsson filtering system, in which the rougher fibers which have not passed through the sieve and remain on the.

surface of the cylindrical, horizontally positioned sieve plate are removed by detaching them by a water spray from the other side of the sieve plate and by conducting them away in an open trough. Furthermore, there are different drumlike sifting devices in which the fibers which have been caught in the sieve and block its holes or crevices are detached with different blades moving in relation to the sieve surface, the blades creating pressure variation which detaches the fibers from the surface. In the latter devices the reject pulp has to pass over the entire sieve surface before it is removed from the sieve. This phenomenon naturally decreases the capacity of the sieve, because one and the same particle may be caught several times in the holes or crevices of the sieve surface before being removed. When the reject pulp moves toward its outlet its connection grows to the extent that the acceptable fibers among the rejects are no longer separated but are removed with the rejects.

Finnish patent No. 43,671 introduces a sifting device which includes,'among other things, a sieve cleaner with spraypipes fitted inside or outside the rotating sieve surface. The spray detaches the fibers caught in the sieve and conducts them to the outlet situatedat some distance from the spray pipes. Besides its complicated structure this construction has a disadvantage in that the outlet trough covers a considerable part of the sieve surface, thereby decreasing the capacity of the sieve.

Also known is a pressuresifting device, which comprises a sieve cylinder and a blade rotating around it which wipes close to the surface of the sieve cylinder on the side of the pulp to be sifted. This rotating blade has a cavity reaching from one end to the other which has a crevice opening towards the sieve cyliner and which is connected with the reject pulp outlet space at one end.

SUMMARY OF THE INVENTION According to the invention there is provided reject detaching means along the leading edge of the sieve cleansing tube opening and blocking means along the opposite edge in order toloosen the reject on the sieve plate and withdraw the reject from the chamber through the sieve cleansing tube.

The following advantages in comparisonwith the previously known sifting devices are gained by a sieve cleaner according to the. invention:

Rough fibers which will not pass through the sieve are all removed from the entire width of the sieve into the outlet pipe of the sieve cleaner, at which time the reject. surface of the sieve is cleaned to receive new, unsifted pulp. In comparison with'known devices, it does not have the pulse blades which often cause rough treatment and press pulp impurities through the sieve plate. j

The advantage of a fixed sieve cleaner with a fixed outlet pipe for reject is a simple structure which makes it easy to control the movement of the particularly difficult flowing reject When a fixed sieve cleaner is used, it is possible to install a spray pipe inside the sieve by simple technique to detach the reject and to improve its flow.

Furthermore, when a rotating sieve drum and a fixed sieve cleaner, the latter being stationary in relation to the accept pipe, are used, an advantage is gained in that the pressure vibration present in the accept pipe is insignificant, essentially less than when using rotating sieve cleaners which move in relation to the accept pipe and which cause in the accept pipe system regular pressure variation depending on the rotational velocity. The said pressure vibration is particularly disadvantageous when assorters are used in the paper manufacturing process before the paper machine head box, in which case the pressure vibration created by the assorters causes harmful variation in the base weight of the paper product.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a vertical section of a device according to the invention;

FIG. 2 shows a horizontal section of the same device;

DESCRIPTION OF THE PREFERRED EMBODIMENT Cylindrical sieve drum 1 rotates in a closed space in the'direction indicated by the arrow (FIG. 2); pulp is fed on the outside of the drum through opening 2. Accept pulp passes through sieve drum 1 and is removed from above at point 3. Rougher reject pulp is caught on the surface of the sieve and moves, following the drum surface, into sieve cleaner 4, where a lower pressure prevails than on the outer surface of the sieve; Sieve cleaner 4 consists of a tubelike part, so-called outlet pipe 5, which is of the length of the height of the sieve drum and open at the side and which collects reject pulp over the entire width of the sieve. To make the removal of reject pulp moreeffective, bladelike detachment device 6 has been connected with the outlet pipe; the pressure variations push the reject pulp from the sieve surface and its crevices. The detached reject pulp follows the inner surface of the blade to outlet pipe 5. Keeping the sieve plate clean is made moreeffective with spray pipe 8 installed inside drum 1; diluting reject pulp at its outlet point spray pipe 8 decreases the amount of accept pulp carried away with the reject. The peripheral velocity of the sieve drum must be high enough to create turbulence on the drum surface to prevent the felting phenomenon. If felting occurs, blades can be placed close to the sieve drum to create pressure impulses directed away from the sieve. Thisv can be accomplished by a means for adjusting the position of the sieve cleansing means, shown as handle 9 attached to the sieve cleansing means.

Blocking piece 7 is meant to keep the pulp flow in the rotational direction of sieve drum 1. That is to say, the blocking piece prevents the pulp from entering the pipe 4 in a direction other than in the rotational direction of sieve platel.

It is obvious that the invention is not limited to the particular form described above but detaching organ 6 can be replaced by, for example, a brush or the like, and can in some cases be eliminated entirely. The same applies to the blocking piece. There is no limitation as to the number of sieve cleaners, and especially in drum sieves with great diameters, several sieve cleaners may be necessary.

What is claimed is:

1. An improved sifting device for pulp and the like having a chamber with inlet means for the pulp; in the chamber and rotatably journalled thereto a cylindrical sieve plate defining an accept collecting space and having outlet means for the accept; means for rotating the cylindrical sieve plate about a vertical axis; and sieve cleansing means fixedly attached to the chamber across the outer sieve plate surface, said sieve cleansing means comprising a pipe having an opening at the side towards the sieve plate surface for removing reject therefrom, the improvement comprising: reject detaching means adjacent said sieve plate and positioned at the front longitudinal edge of the pipe, and in communication with said opening blocking means at the rear longitudinal edge of the pipe for substantially preventing the pulp feed from moving other than in the rotational direction of said sieve plate, said blocking means being adjacent said sieve plate, said detaching and blocking means positioned wholly at opposite sides of the pipe opening and in spaced relation to said sieve plate.

2. The improved sifting device of claim 1, wherein the detachment means comprises a wing with a front side closer to the sieve plate than its rear side in order to create suction on the sieve plate surface.

3. The improved sifting device of claim 2 wherein said detaching means has a generally triangular crosssection.

4. The improved sifting device of claim 2, wherein only one side of said detaching means is adjacent the sieve plate. 5

5. The improved sifting device of claim 1, further comprising a spray pipe attached to the chamber inside the cylindrical sieve plate opposite and along the sieve cleansing means.

6. The improved sifting device of claim 1, in which the inlet means for the pulp comprises an inlet in the cylindrical vertical wall of the chamber; the outlet means for the accept comprises a central outlet in one of the chamber end walls; and the cylindrical sieve plate is adapted to be rotated about a vertical central axis.

7. The improved sifting device of claim 1, further comprising means for arbitrarily adjusting the position of the blocking and detaching means in relation to the sieve plate.

8. The improved sifting device of claim 1, wherein said detaching means and said blocking means extend axially of and are attached to said pipe.

9. The improved sifting device of claim 1, wherein said pipe opening is positioned between said detaching means and said blocking means and extends axially of said pipe along the entire length of said cylindrical sieve plate. 

1. An improved sifting device for pulp and the like having a chamber with inlet means for the pulp; in the chamber and rotatably journalled thereto a cylindrical sieve plate defining an accept collecting space and having outlet means for the accept; means for rotating the cylindrical sieve plate about a vertical axis; and sieve cleansing means fixedly attached to the chamber across the outer sieve plate surface, said sieve cleansing means comprising a pipe having an opening at the side towards the sieve plate surface for removing reject therefrom, the improvement comprising: reject detaching means adjacent said sieve plate and positioned at the front longitudinal edge of the pipe, and in communication with said opening blocking means at the rear longitudinal edge of the pipe for substantially preventing the pulp feed from moving other than in the rotational direction of said sieve plate, said blocking means being adjacent said sieve plate, said detaching and blocking means positioned wholly at opposite sides of the pipe opening and in spaced relation to said sieve plate.
 2. The improved sifting device of claim 1, wherein the detachment means comprises a wing with a front side closer to the sieve plate than its rear side in order to create suction on the sieve plate surface.
 3. The improved sifting device of claim 2 wherein said detaching means has a generally triangular cross-section.
 4. The improved sifting device of claim 2, wherein only one side of said detaching means is adjacent the sieve plate.
 5. The improved sifting device of claim 1, further comprising a spray pipe attached to the chamber inside the cylindrical sieve plate opposite and along the sieve cleansing means.
 6. The improved sifting device of claim 1, in which the inlet means for the pulp comprises an inlet in the cylindrical vertical wall of the chamber; the outlet means for the accept comprises a central outlet in one of the chamber end walls; and the cylindrical sieve plate is adapted to be rotated about a vertical central axis.
 7. The improved sifting device of claim 1, further comprising means for arbitrarily adjusting the position of the blocking and detaching means in relation to the sieve plate.
 8. The improved sifting device of claim 1, wherein said detaching means and said blocking means extend axially of and are attached to said pipe.
 9. The improved sifting device of claim 1, wherein said pipe opening is positioned between said detaching means and said blocking means and extends axially of said pipe along the entire length of said cylindrical sieve plate. 